Insulator



G.- FACCIOLI April 22. 1924.

INSULATOR Filed Nov. 8, 1918 w ...w n www MF e A ve nmv. w

Patented Apr. 22, 1924.

UNITED STATES PTENT OFFICE.

GIUSEPPE FACCIOLI, OF PITTFIELD, MASSACHUSETTS, ASSIGNO'R T GENERAL ELEC- TRIO COMPANY CORPORATION OF NEW YORK.

INSULATOR.

Application filed November 8, 1918. Serial Ho. 281,597.

To all whom it may camera:

Be it known that I, Grusnrrn FAooIoLI, a citizen of the United States, residin at Pittsfield, in the county of Berkshire, tate of Massachusetts, have invented certain new and useful Improvements in Insulators, of

which the following is a specification.

My invention relates to insulators for electrical conductors and particularly to insulators of the type known as bushings which provide for the insulation of a conductor more or less completely surrounded by another conductor at a materially difierent potential. An object of my invention is to reduce the size of insulators, articularly the length thereof. I accomp ish the objects of my `invention by modifying the electrostatic flux distribution in a 'desired manner so as to secure generally a more uniform distribution of the potential over the surface or surfaces of the insulating ;nass of the insulator.

In substantially all insulators there are two ways in which the insulator may' fail: 1st, by breakdown through the insulating material; 2d, by creepage or arcing over the surface or surfaces of the insulating material. Quite generally the prevention of arcing or creepage over the insulating material determines to a material extent the size of the insulator, and particularly the length of the insulating mass. Generally, also, unless some means is provided to equalize the potential r unit of length, or gradient over the sur ace of the insulating mass, the potential will be distributed over the surface of the insulating mass in a very un-uniform manner, some portions of the surface of the insulatin mass bein sub- ]'ected to materially hig er potentia s per unit length than other portions. It is of course necessary so to design the insulator, and make it of such size, and length in particular, that the average potential at no point on the insulator surface exceeds 'a certain safe value. Hence, when the potential is not uniformly distributed over a surface of the insulator, the insulator must be given a'g'reater size than if the potential were distributed substantially uniformly.

In the practice of my invention, I provide means by which it is possible to equalize the potential per unit length over the insulating mass between the conductors, and to distribute the potential over the surface or surmembers may be a plurahty of metallic petticoats of such sizes and so spaced and related to the conduotors as to receive the desired potentials.

For a more complete understanding of the nature and objects of my invention reference should be had to the following detailed description, taken in connection with the accompanying drawing in which Fig. 1 shows an insulatmg bushing, partly in section, embodying my invention; while Fig. 2 shows a modified form.

Referring now to Fig. 1, 10 represents an electrical conductor, such as a lead for encased high tension electrical apparatus, and 11 represents 'an electrical conductor or structure at` a materially different potential from the lead 10, which surrounds the lead 10, and frequently is and will here be su posed to be in conducting relation with ti: casing for enclosed electrical apparatus, from which casing the lead 10 is to be insulated.

12 denotes the upper insulating member comprising a portion of an insulating bush-4 ing which may be'of molded porcelain, and 13 denotes the lower member.

The lead or conductor 10 is secured in a suitable manner in the insulating bushng, which may be solid or filled with .an insulating medium, such as oil or insulating compound here indicated at 14.

In the further description of the bushing shown in the drawing, I will describe my invention as applied only to the upper insulating member 12 because the lower member is usually submerged in oil although obviously my invention is equally applicable to the lower member when it is not so submerged, as for instance, when it passes through the wall or roof of a building.

To alter the potential at one or more points on the surface of the insula-ting member 12, I lace thereon one or more conducting annu ar members or rings such as are shown at 15, 16, 17, 18, 19 and 20. These members are referably secured beneath the surface of tlie insulating member 12 as shown, and are so sha that they do not coincide with any of t e natural system of equipotentia'l surfaces drawn for the unmodified otential distribution, such as are indicated y S and S', and shown as intersecting the insulating surface at points a and b where certain of the annular conduc in members are applied.

y suitably Shaping such conducting members and dis osing them with respect to the conductors t emselves I alter the electrostatic flux and, con uently, the distribution of potential alongt ie surface of the insulating member 12 between the conductors 10 and 11. By properly selecting the size, deflection and distribution of these conducting annular members, I am enabled to curc a desired distribution of potential over the surface of the bushin as will be more readily understood from t e following considerei tion.

`Su pose now that no conductin members have een provided along the sur ace of the insulating member 12 between the conductors 10 and 11 and that there is a potential difference of 100,000 volts between conductors 10 and 11, the conductor 11 being at ground potential, and that the potential diference from conductor 11 to point a is 60,000 volts, and further suppose that the point a is half way along the distance over the surface of member 12, between the conductors 10 and 11. It may be imagined that the capacity between the conductors 10 and 11 is composed of two capacities in series; that is, the capacity between the conductor 10 and the point a and the capacity between the point a and the conductor 11. Then, in accordance with the well known law of electrostatics, the potentials on each side of point a are in inverse proportion to the capacities on each side thereof, i. e., inversely proportional to the capacities naturally on the respective sides of the unmodified equi- [cxtential surface S passing through point a. nsequently, if V1 denotes the otential from conductor 10 to point a an Cl the corresponding capacity, and if Vz denotes the potential from point a to conductor 11, and C, the corresponding capacity, we would have f` Vf, 60,000 which shows, according to the above supposition, that the natural capacityv between the surface S and the conductor 10 is one and a half times greater than that between the surface S and the conductor 11. Then, to proportion relatively the potential distribution on the two sides of point a, it is necessary to increase the last referred to capacity, or that denoted C2 in the above formula, by an amount substantially one-half its original value in order to be equal to that on the other side of surface S. Obviously, this can be done by connecting a condenser having this required capacity from point a to the conducting structure 11, (that is, in parallel with the natural capacity 0,); but as above noteti this increase in capacity is preferably to be accom lished by suitably Shaping and disposing t e annular conducting member secured at a, here denoted as member 17.

It is to be oberved that if member 17 was so shaped that its surface coincided with the surface S, there would be no alteration of the electmtatic line of force traversing the surface S and conse uently no change in the ca aci `dl' potentia distribution on the two si es o point a. If though, the surface of member 17 is bent downwardly away from the natural equipotential surface S, 'as shown, a greater effective surface of the member 17 is presented to the conducting structure 11 so that the ca acitI from surface S to this structure is t ereby increased in an amount depending on the bending; the angle through which it is defiected or bent .bein determined by the capacity it is desir to add.

By a repetition of this process of bending the conducting members intermediate point a and the conductors 10 and 11, through determinable angles out of the natural equipotential surfaces intersectin the insulating surface at the points where t ey are ap lied, the capacities between each point ying along a line in an axial plane of the insulator,'may be as nearly proportionately distributed as may be desired, consequently the average face will ave been approximately equalized for all points in this manner.

The function of the conducting annular members 15 to 20 may be explained in another pmanner. Assuming as before that without these members, the potential at the ,point a is 60,000 when there is a potential ifl'erence of 100,000 between the conductors 10 and 11. A potential of 50,000 is desired at the ploint a as this point is half way between t e conductors 10 and 11; The annular member 17 is applied at the point a and deflected as shown away from the natural euipotential surface S and into a region o naturally lower otential. ductin material, t e entire annular member 17 wi assume the same potential and this will be the average'of the natural electrostatic field throu h which this member 17 extends. The deection and the extent of the member 17 is therefore so determined that it must assume' the desired potential of 50,000. Other points along the surface of the insulating member 12 are bron ht to deotential over the insulating sur- Being of con- 3 sired potentials in similar manner y applyi ing at such points other conducti annular members of suitable extent and de ection.

The conducting rings distributed over the insulating surface may in some instances be designed to serve not only as a means for equa izing the potential distribution over such surface but also as a tticoat structure. This use of conducting rings secured to the surface of the'insulati member has' been illustrated in Fig. 2. ere the rings 15' to 21' are given a downwardly sloping direction which rmits rain and falling particles to freely glide ofl' the insulating structure.

Having now described what is at present the best means known to me for carryin out an embodiment of my invention, I woul have it undersbood that such means are merely illustrative and that I do not mean to be limited thereby shown nor in the choice of recognized equivalents except as defined in my claims hereunto appended.

What I believe as new and desireto secire by Letters Patent of the United States, i

1. The combination with two adjacent conductors, of a mass of insulating material therebetween to insulate each from the other, and a pluralit)r of conducting members 'extendin outwardly from an outer surface of sai insulatin material between the two conductors, 'saidg conducting members being extended and deflected to disto -the exact details tribute a potential difference between said conductors substantially uniformly along said surface.

2. The combination with a conductor, of an annular conductor surronndingthe same intermediate its length, insulating material between said conductors for insulating each from the other, and a plurality of conical rin of conducting material surrounding sai first named conductor and extending outwardl from a surface of said insulating material between said conductors, said rings being extended and deflected bo distribute a potential difference between said conductors substantially' uniformly along said surface.

3. The combination with a substantially linear conductor, of a conducting structure surrounding the same intermediate its length,

insulating members secured between said' conductor and each side of the structure thereby forming a bushing, and a plurality of comcal rings of conducting material extending outwardly from the surface of the bushing at redetermined points, said rings being extened and deflected to distribute a potential difl'erence between said conductor and conducting structure substantially uniformly along said surface.

In witness whereof, I have hereunto set niy hand this second day of November, 1918.

\ GIUSEPPE FACCIOLI. 

